*{
   margin: 0;
   padding: 0;
}
ul{
    list-style: none;
}
a{
    color: #333;
}
#nav{
    background-color: #333;
}
#nav > div{
    width: 1000px;
    margin: 0 auto;
    height: 50px;
    line-height: 50px;
    color: #fefefe;
    display: flex;
    justify-content: space-between;
    align-items: center;
}
#nav ul{
    display: flex;
}

#nav a{
    color: #fefefe;
    text-decoration: none;
    padding: 0 10px;
}
main{
    width: 1000px;
    margin: 0 auto;
}
main > nav ul{
    display: flex;
    padding-top: 20px;
    border-bottom: 1px solid #ddd;
}
main > nav li{
    margin-right: 15px;
    height: 45px;
    line-height: 45px;
}
.content{
    display: flex;
    justify-content: space-between;
    flex-wrap: wrap;
    padding-top: 30px;
}
.content li{
    width: 24%;
    border: 1px solid #ddd;
    padding: 8px;
    box-sizing: border-box;
    border-radius: 4px;
    margin-bottom: 20px;
}
.content li img{
    width: 100%;
}
.content h3{
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}
.content p {
    margin: 5px 0;
}